Chapter 7 Photosynthesis: Using Light to Make Food PowerPoint Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition Eric J. Simon, Jean L. Dickey, and Jane B. Reece Lectures by Edward J. Zalisko
Biology and Society: Biofuels Wood has historically been the main fuel used to produce heat and light.
Figure 7.0
Biology and Society: Biofuels Industrialized societies replaced wood with fossil fuels including coal, gas, and oil. To limit the damaging effects of fossil fuels, researchers are investigating the use of biomass (living material) as efficient and renewable energy sources.
Biology and Society: Biofuels There are several types of biofuels. Bioethanol is a type of alcohol produced by the fermentation of glucose made from starches in crops such as grains, sugar beets, and sugar cane. Bioethanol may be used directly as a fuel source in specially designed vehicles or as a gasoline additive.
Biology and Society: Biofuels Cellulosic ethanol is a type of bioethanol made from cellulose in nonedible plant material such as wood or grass. Biodiesel is made from plant oils or recycled frying oil.
THE BASICS OF PHOTOSYNTHESIS Photosynthesis is used by plants, algae (protists), and some bacteria, transforms light energy into chemical energy, and uses carbon dioxide and water as starting materials.
THE BASICS OF PHOTOSYNTHESIS The chemical energy produced via photosynthesis is stored in the bonds of sugar molecules. Organisms that use photosynthesis are photosynthetic autotrophs and the producers for most ecosystems.
Figure 7.1 LM Plants (mostly on land) PHOTOSYNTHETIC AUTOTROPHS Photosynthetic Protists (aquatic) Photosynthetic Bacteria (aquatic) Forest plants Kelp, a large, multicellular alga Micrograph of cyanobacteria
Figure 7.1a Plants (mostly on land) Forest plants
Figure 7.1b Photosynthetic Protists (aquatic) Kelp, a large, multicellular alga
LM Figure 7.1c Photosynthetic Bacteria (aquatic) Micrograph of cyanobacteria
Chloroplasts: Sites of Photosynthesis Chloroplasts are the site of photosynthesis and found mostly in the interior cells of leaves. Inside chloroplasts are interconnected, membranous sacs called thylakoids, which are suspended in a thick fluid called stroma. Thylakoids are concentrated in stacks called grana.
Chloroplasts: Sites of Photosynthesis The green color of chloroplasts is from chlorophyll, a light-absorbing pigment that plays a central role in converting solar energy to chemical energy. Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits.
Figure 7.2-3 LM Colorized TEM Photosynthetic cells Vein Chloroplast Inner and outer membranes Stroma Thylakoid space Granum CO 2 O 2 Stomata Leaf cross section Interior cell
The Simplified Equation for Photosynthesis In the overall equation for photosynthesis, notice that the reactants of photosynthesis are the waste products of cellular respiration.
Figure 7-UN01 Light energy 6 CO 2 6 H 2 O C 6 H 12 O 6 Photosynthesis Carbon dioxide Water Glucose 6 O 2 Oxygen gas
The Simplified Equation for Photosynthesis In photosynthesis, sunlight provides the energy, electrons are boosted uphill and added to carbon dioxide, and sugar is produced.
The Simplified Equation for Photosynthesis During photosynthesis, water is split into hydrogen and oxygen. Hydrogen is transferred along with electrons and added to carbon dioxide to produce sugar. Oxygen escapes through stomata into the atmosphere.
A Photosynthesis Road Map Photosynthesis occurs in two multistep stages: 1. the light reactions convert solar energy to chemical energy and 2. the Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide.
A Photosynthesis Road Map The initial incorporation of carbon from the atmosphere into organic compounds is called carbon fixation. This lowers the amount of carbon in the air. Deforestation reduces the ability of the biosphere to absorb carbon by reducing the amount of photosynthetic plant life.
Figure 7.3-2 Light H 2 O Chloroplast CO 2 Light reactions NADP + ADP P Calvin cycle ATP NADPH O 2 Sugar
THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Chloroplasts are chemical factories powered by the sun and convert sunlight into chemical energy.
Figure 7-UN02 Light H 2 O CO 2 Light reactions NADP ADP + P ATP NADPH Calvin cycle O 2 Sugar
The Nature of Sunlight Sunlight is a type of energy called radiation, or electromagnetic energy. The distance between the crests of two adjacent waves is called a wavelength. The full range of radiation is called the electromagnetic spectrum.
Figure 7.4 Increasing wavelength 10 5 nm 10 3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 3 m Gamma rays X-rays UV Infrared Microwaves Radio waves Visible light 380 400 500 600 700 750 Wavelength (nm) Wavelength 580 nm
Figure 7.5 Light Chloroplast Reflected light Absorbed light Transmitted light (detected by your eye)
The Process of Science: What Colors of Light Drive Photosynthesis? Observation: In 1883, German biologist Theodor Engelmann saw that certain bacteria tend to cluster in areas with higher oxygen concentrations. Question: Could this information determine which wavelengths of light work best for photosynthesis? Hypothesis: Oxygen-seeking bacteria will congregate near regions of algae performing the most photosynthesis.
The Process of Science: What Colors of Light Drive Photosynthesis? Experiment: Engelmann laid a string of freshwater algal cells in a drop of water on a microscope slide, added oxygen-sensitive bacteria to the drop, and used a prism to create a spectrum of light shining on the slide.
The Process of Science: What Colors of Light Drive Photosynthesis? Results: Bacteria mostly congregated around algae exposed to redorange and blue-violet light and rarely moved to areas of green light. Conclusion: Chloroplasts absorb light mainly in the blue-violet and red-orange part of the spectrum.
Number of bacteria Figure 7.6 Light Prism Microscope slide Bacteria Bacteria Algal cells 400 500 600 700 Wavelength of light (nm)
Chloroplast Pigments Chloroplasts contain several pigments: 1. Chlorophyll a absorbs mainly blue-violet and red light and participates directly in the light reactions. 2. Chlorophyll b absorbs mainly blue and orange light and participates indirectly in the light reactions.
Chloroplast Pigments Carotenoids absorb mainly blue-green light, participate indirectly in the light reactions, and absorb and dissipate excessive light energy that might damage chlorophyll. The spectacular colors of fall foliage are due partly to the yellow-orange light reflected from carotenoids.
Figure 7.7
How Photosystems Harvest Light Energy Light behaves as photons, a fixed quantity of light energy. Chlorophyll molecules absorb photons. Electrons in the pigment gain energy. As the electrons fall back to their ground state, energy is released as heat or light.
Figure 7.8 Absorption of a photon excites an electron. e Excited state The electron falls to its ground state. Light Heat Photon Chlorophyll molecule Light (fluorescence) Ground state (a) Absorption of a photon (b) Fluorescence of a glow stick
How Photosystems Harvest Light Energy In the thylakoid membrane, chlorophyll molecules are organized with other molecules into photosystems. A photosystem is a cluster of a few hundred pigment molecules that function as a lightgathering antenna.
How Photosystems Harvest Light Energy The reaction center of the photosystem consists of chlorophyll a molecules that sit next to another molecule called a primary electron acceptor, which traps the light-excited electron from chlorophyll a. Another team of molecules built into the thylakoid membrane then uses that trapped energy to make ATP and NADPH.
Figure 7.9 Chloroplast Cluster of pigment molecules Photon e Electron transfer Primary electron acceptor Reactioncenter chlorophyll a Reaction center Thylakoid membrane Transfer of energy Photosystem Pigment molecules
How the Light Reactions Generate ATP and NADPH Two types of photosystems cooperate in the light reactions: 1. the water-splitting photosystem and 2. the NADPH-producing photosystem.
Figure 7.10-3 Primary electron acceptor 2 Energy to make ATP Primary electron acceptor 2e 2e 3 NADP NADPH 2e Light Light 1 Reactioncenter chlorophyll H 2 O 1 2 2e 2 H O 2 Reactioncenter chlorophyll Water-splitting photosystem NADPH-producing photosystem
How the Light Reactions Generate ATP and NADPH The light reactions are located in the thylakoid membrane. An electron transport chain connects the two photosystems and releases energy that the chloroplast uses to make ATP.
Figure 7.11 To Calvin cycle Light H Light NADPH NADP ADP P H ATP Stroma Thylakoid membrane Photosystem Electron transport chain Photosystem ATP synthase Inside thylakoid H 2 O 1 2 2e O 2 H H H H Electron flow H Thylakoid membrane
Figure 7.12 e ATP e e NADPH e e e e Water-splitting photosystem NADPH-producing photosystem
Figure 7-UN06 ADP ATP e acceptor 2e NADP e acceptor 2e 2e NADPH Photon Photon Chlorophyll H 2 O 2e Chlorophyll NADPH-producing photosystem 2 H + 1 2 O 2 Water-splitting photosystem
THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE The Calvin cycle functions like a sugar factory within a chloroplast and regenerates the starting material with each turn.
Figure 7-UN03 Light H 2 O CO 2 Light reactions NADP ADP + P ATP NADPH Calvin cycle O 2 Sugar
Figure 7-UN07 CO 2 ATP NADPH Calvin cycle ADP NADP P G3P P Glucose and other compounds (such as cellulose and starch)
Figure 7.13-4 CO 2 (from air) P 1 RuBP sugar 4 ADP P ATP P Calvin cycle P Three-carbon molecule ATP ADP P NADPH G3P sugar 3 P P NADP G3P sugar 2 G3P sugar P Glucose (and other organic compounds)
Figure 7-UN05 Chloroplast Light H 2 O CO 2 Stack of thylakoids Light reactions NADP ADP P ATP Calvin cycle Stroma NADPH O 2 Sugar Sugar used for cellular respiration cellulose starch other organic compounds
Evolution Connection: Solar-Driven Evolution C 3 plants use CO 2 directly from the air and are very common and widely distributed.
Evolution Connection: Solar-Driven Evolution C 4 plants close their stomata to save water during hot and dry weather and can still carry out photosynthesis. CAM plants are adapted to very dry climates and open their stomata only at night to conserve water.
Figure 7.14 ALTERNATIVE PHOTOSYNTHETIC PATHWAYS C4 Pathway (example: sugarcane) CAM Pathway (example: pineapple) Cell type 1 CO 2 CO 2 Night Four-carbon compound Four-carbon compound Cell type 2 CO 2 CO 2 Calvin cycle Calvin cycle Sugar C 4 plant Sugar CAM plant Day